Field of the Invention
The present invention relates to a variable magnification optical system and an image pickup apparatus using the same.
Description of the Related Art
As a variable magnification optical system, a variable magnification optical system which includes four lens units, or a variable magnification optical system which includes five lens units, has been known.
In Japanese Patent No. 5893959 Publication (first example), a variable magnification optical system which includes five lens unit has been disclosed. This variable magnification optical system includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a negative refractive power.
In Japanese Patent No. 5006076 Publication (second example), a variable magnification optical system which includes four lens units has been disclosed. This variable magnification optical system includes a first unit which is fixed at the time of zooming, a second unit having a negative refractive power, a third unit having either a positive refractive power or a negative refractive power, a fourth unit which includes an aperture stop and which is fixed at the time of zooming.
In Japanese Patent No. 5426653 Publication (fourth example), a variable magnification optical system which includes five lens units has been disclosed. This variable magnification optical system includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power.